Glycerol facilitator

Baker, M.E. Saier, M.H. (1990). A common ancestor for bovine lens fiber major intrinsic protein, soybean nodulin-26 protein, and E. coli glycerol facilitator. Cell 60, 185-6. 

Figure 7.1. Mechanism of uptake and initial enzymatic reactions in the microbial metabolism of glycerol (G). Note The gene products GlpF, GlpK, GlpD correspond to a glycerol facilitator protein, glycerol kinase, and glycerol 3-phosphate dehydrogenase, respectively.

THE GLYCEROL FACILITATOR GIpF, ITS AQUAPORIN FAMILY OF CHANNELS, AND THEIR SELECTIVITY... 

Maurel, C., Reizer, J., Schroeder, J. I., Chrispeels, M. J., and Saier, M. H., Jr. (1994). Functional characterization of the Escherichia coli glycerol facilitator, GlpF, in Xenopus oocytes./ Biol. Chem. 269, 11869-11872. 

Detailed structural data are only available for a few highly selective charmels. The best characterized is the model system gramicidin, which has been elucidated using NMR-based techniques [14,15]. Among physiological systems, atomic level resolution structures (based on x-ray or cryoelectron microscopy) are available for a potassium channel from S. lividans (KcsA) [5], two prokargotic chloride channels [16], a stretch activated channel from M. tuberculosis [17], human red cell aquaporin-1 [18], and a glycerol facilitator from... 

Note that many of the molecules produced have few internal polar fimctional groups to which ions may bind. Instead, it is more likely that ion-water-channel interactions escort the ion through the pore. To that end. many of the models can then be viewed as methods to pull water into the lipidic core of a bilayer membrane and thereby stabilize ions in transport. Recent studies of molecular dynamics simulations of ion transportation in human aquaporin-1 and in the bacterial glycerol facilitator GlpF revealed the key role of water in the stabilization of ions in transit and in the molecular selectivity of channels. Synthetic compoxmds form less-defined stmctures than these complex proteins but apparently act as efficiently as more complex natural materials. It is likely that continued study of synthetic systems will continue to reveal the general details underlying all transport processes. 

The MIP (major intrinsic protein TC 1.A.8 in the Transporter Classification Database (TCDB www.tcdb.org)) family of aquaporins and glycerol facilitators were found in the 11 bacteria originally studied. Proteins in this family facilitate the passage of several neutral molecules such as water, glycerol, dihydroxyacetone, CO, urea, and ammonia (Jensen et al. 2002 Carbrey et al. 2003 Uehlein et al. 2003). All the microorganisms analyzed have at least one member of this family while some have up to five members (Table 4.1). 

Table 4.1. Summary of functionally characterized aquaporins and glycerol facilitators in LAB.

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